How to get pixel color from SKSpriteNode or from SKTexture?

Question

I want to get the exact selection of my object on the game map. An object is a sprite with which there are transparent pixels, and I want to check the touch location for these transparent pixels. Any clue?

Answer 1

In the Sprite Kit, you do not have access to texture data.

Instead, you will need to create a bitmask from the image, for example, loading the image as a UIImage or CGImage and scanning for all opaque pixels.

Answer 2

You can subclass SKSpriteNode, add a link to the image and check the alpha of this image when it detects touches.

1) Add an instance variable to save the image

@implementation DraggableSprite { UIImage *_holdingImage; } 

2) Then in the init method you can save a link to this image

 -(id)initWithImageNamed:(NSString *)name { if (self=[super initWithImageNamed:name]) { self.userInteractionEnabled = YES;//enable touches handling self.anchorPoint = P(0,0); _holdingImage = [UIImage imageNamed:name]; } return self; } 

3) Touch Detection

 -(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; CGPoint positionInScene = [touch locationInNode:self]; CGFloat a = [UIImage getAlphaFromImage:_holdingImage atX:positionInScene.x andY:self.size.height-positionInScene.y]; NSLog(@"alpha is %f",a); } 

4) Alpha Check Function

 +(CGFloat)getAlphaFromImage:(UIImage*)image atX:(NSInteger)xx andY:(NSInteger)yy { // Cancel if point is outside image coordinates if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), CGPointMake(xx,yy))) { return 0; } // Create a 1x1 pixel byte array and bitmap context to draw the pixel into. // Reference: http://stackoverflow.com/questions/1042830/retrieving-a-pixel-alpha-value-for-a-uiimage NSInteger pointX = xx; NSInteger pointY = yy; CGImageRef cgImage = image.CGImage; NSUInteger width = image.size.width; NSUInteger height = image.size.height; CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); int bytesPerPixel = 4; int bytesPerRow = bytesPerPixel * 1; NSUInteger bitsPerComponent = 8; unsigned char pixelData[4] = { 0, 0, 0, 0 }; CGContextRef context = CGBitmapContextCreate(pixelData, 1, 1, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); CGColorSpaceRelease(colorSpace); CGContextSetBlendMode(context, kCGBlendModeCopy); // Draw the pixel we are interested in onto the bitmap context CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height); CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage); CGContextRelease(context); CGFloat alpha = (CGFloat)pixelData[3] / 255.0f; return alpha; } 

Answer 3

Here's how to get the color of one pixel directly from SKTexture:

 class SpriteKitUtility { class func pixelFromTexture(texture: SKTexture, position: CGPoint) -> SKColor { let view = SKView(frame: CGRectMake(0, 0, 1, 1)) let scene = SKScene(size: CGSize(width: 1, height: 1)) let sprite = SKSpriteNode(texture: texture) sprite.anchorPoint = CGPointZero sprite.position = CGPoint(x: -floor(position.x), y: -floor(position.y)) scene.anchorPoint = CGPointZero scene.addChild(sprite) view.presentScene(scene) var pixel: [Byte] = [0, 0, 0, 0] let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue) let context = CGBitmapContextCreate(&pixel, 1, 1, 8, 4, CGColorSpaceCreateDeviceRGB(), bitmapInfo); UIGraphicsPushContext(context); view.drawViewHierarchyInRect(view.bounds, afterScreenUpdates: true) UIGraphicsPopContext() return SKColor(red: CGFloat(pixel[0]) / 255.0, green: CGFloat(pixel[1]) / 255.0, blue: CGFloat(pixel[2]) / 255.0, alpha: CGFloat(pixel[3]) / 255.0) } }